PROJECT SUMMARY/ABSTRACT The mechanisms that control hepatic stellate cell (HSC) migration during liver development and regeneration are not well understood. This knowledge gap has hindered the generation of new therapies and the improvement of patient outcome for various developmental disorders such as congenital hepatic fibrosis and fibrosing liver diseases such as alcoholic and non-alcoholic steatohepatitis. The critical need addressed in this proposal is to identify and characterize factors that influence HSC migration during development and in regeneration. HSCs migrate to the liver from the septum transversum early in vertebrate development. Once in the liver, HSCs secrete growth factors and cytokines, such as TGF- and FGF10, that promote hepatocyte proliferation. In the healthy adult liver, HSCs? main function is to act as a storage site for vitamin A and regulate extracellular matrix (ECM) turnover. When the liver is injured, HSCs migrate to the liver injury site where they secrete ECM, growth factors, and cytokines to promote liver regeneration. Little is known about the factors involved in HSC migration into the liver during development and throughout the liver in response to injury. My long-term goal is to define mechanisms of liver development and regeneration, providing a foundation for improved therapies and patient outcomes for congenital disorders and fibrotic liver diseases. The overall objective of this proposal is to define mechanisms that control HSC behavior during development and regeneration. The central hypothesis in this proposal is that podxl regulates HSC migration to the liver during normal development (Aim 1), and within the liver in response to injury (Aim 2). Podxl is a highly sialylated and glycosylated transmembrane protein that is known to promote migration of several cell types, including hematopoietic stem cells and cancer cells. Several studies have shown that podxl is highly expressed in zebrafish HSCs, and our preliminary data demonstrates that knockdown of podxl in zebrafish during development results in fewer HSCs in the liver. In this study, the aim is to determine the role of podxl in HSCs during development and regeneration. A podxl mutant and overexpression line will be created to determine the role and mechanism of podxl in development. The working hypothesis is that Podxl promotes HSC migration by interaction of its DTHL motif with the actin-binding protein Moesin. In addition, homologous recombination will be used to create an HSC-specific Cre line that can be used to knock down genes in HSCs. This new HSC expressing Cre line will be used to knock down podxl in HSCs and determine how that influences their migration to liver injury sites and subsequent hepatocyte proliferation. This project involves generating novel genetic and imaging tools, which will be instrumental for my career development. Understanding the role of podxl in HSC migration during development and regeneration is significant because it will provide a foundation for generating new treatments for chronic liver diseases.